------- Comment #10 from steven at gcc dot gnu dot org 2007-11-28 22:02 ------- > + for (defs = DF_INSN_DEFS (insn); > + *defs && DF_REF_REGNO (*defs) != REGNO (x); > + defs++) > + ;
Are you aware of df_find_def() ? > + if (minus_elt) > + cmp = cse_find_comparison_use (dest, insn); Formatting. IMNSHO, computing DEF-USE chains for this niche optimization loses in the cost/benefit trade-off. The whole patch looks like a hack to me to specifically deal with this particular bug report. You could, of course, show that this is actually a very important optimization... I wonder if you can't just integrate this optimization in cse.c as-is by recording an equivalence "a < b" == "signof(c)" when you process "a - b". In any case, adding this optimization to cse.c is Just Wrong (tm). I don't understand why you didn't even try to optimize this in one of the tree optimizers instead. I thought it was clear GCC is trying to reduce its dependency on RTL optimizations? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3507
